The scope of application of tubular films that have, for example, one olefin homo- or copolymer layer such as a polyethylene (PE) layer and a polyamide (PA) layer, for example, is very big. Apart from the packaging industry, one of the areas in which they are used is in the tube lining process for trenchless sewage pipe renovation. Here, it is known from the glass fiber tube liner system that uses UV or steam curing, for example, that a thick-walled PE film having a high density (HDPE—high density polyethylene) is introduced as sliding film, which is—at least in the cross-sectional form of a half circle—positioned tightly against the inner wall of the pipe. Afterwards, a flexible insertion tube executed as tubular film tube is introduced into the pipe (drawing-in process) and the insertion tube slides over the sliding film. This, on the one hand, prevents the tube's inner wall or objects inside the pipe from damaging the insertion tube, and on the other hand considerably lowers the friction generated between the insertion tube and the sliding film, thus facilitating the drawing in of the insertion tube.
In the glass fiber tube liner system cured with UV or steam, such an insertion tube (tube liner) typically has an external tube (outer tube film) executed as tubular film and an internal tube (inner tube film) executed as tubular film. Between them, a carrier material (e.g. glass fibers) impregnated with reactive plastic resin is introduced. Some of the reactive plastic resins used are, for example, commercially available UP resins (polyester or unsaturated polyester resins), VE resins (vinyl ester resins) or EP resins (epoxy resins). UP or VE resins are cured, for example, with the help of photoinitiators, but also thermally. Once inside the pipe, the insertion tube is inflated from the inside with compressed air against the mechanically stable inner tube film until the outer tube film presses tightly against the pipe's inner wall or the sliding film so the resin can be cured afterwards—for example with UV light from a UV light source being slowly pulled through the interior of the inflated insertion tube. Finally, the inner tube film of the insertion tube is pulled out and removed. To do this, a good release effect is necessary so the inner tube film can be pulled out without residues from the cured resin. The layer with the carrier material is then exposed to the substances to be guided through the pipe.
To prevent an unintended, premature curing of the plastic resin before insertion into the pipe to be renovated (particularly during storage), it is necessary for the outer tube film of the insertion tube to have or be made from a protective layer to prevent UV radiation or shorter wavelength radiation of visible light to affect the resin and thus to prematurely harden it. On the other hand, the inner tube film of such an insertion tube must be highly permeable to UV radiation and shorter wavelength radiation of visible light to make the curing process possible—in which a radiation source acts on the tube liner inflated inside the pipe when pulled along the interior of the tube liner, i.e. inside the inner tube film.
Instead of the sliding film described above—and especially in the plastic fiber-tubular film system with warm water or steam curing—a preliner (also known as preliner film) is introduced into the pipe to be renovated. The preliner, typically made of high density polyethylene (HDPE), is a thick-walled film that lines the pipe completely and also prevents direct contact of the tube liner with the pipe's inner wall. To do this, the preliner is placed directly against the pipe's inner wall. Afterwards, the pipe liner is drawn in (drawing-in process) or inverted (inversion process). The preliner prevents, for example, the plastic resin of the tubular liner from adhering to the sewer channel and the still unhardened resin from touching dirt and water. Furthermore, the preliner film also prevents resin from escaping out of the sewer renovation system and contaminating the soil and groundwater. The preliner film also protects the feeds from penetrating excess resin so no resin plugs and obstructions can form. In the drawing-in process, a preliner can also take over a similar function as the sliding films described above used for the pipe liner to be drawn in. In this case, the low coefficients of friction occurring between the sliding film or the preliner and the external film of the pipe liner are essential. As a result of this, the insertion tube or pipe liner is not damaged by the pipe's inner wall or objects inside the pipe when it is drawn into it; on the other hand, the friction between pipe liner and sliding film or preliner is very low and insertion drawing-in of the pipe liner is facilitated.
According to the former description, it is important during drawing-in in the glass fiber tubular liner system, for example, for the coefficient of friction of the internal side of the preliner or sliding film to be very low when moving against the outer film of the tubular liner.
Going back to the tubular liner and, in particular, to its inner tube film, a disadvantage of the PE/PA or PE/AP/PA film (AP: adhesion promoter) used so far as inner tube film mentioned above is its excessively low release effect against adhesive resins. In the worst case scenario, a poor release effect of the inner tube film when pulled out of the cured tubular liner causes the inner tube film to tear off owing to excessive adhesion to the resin because it cannot be removed fully without leaving a residue. The film fragments are thus left behind inside the sewer pipe and can then either block it or act as interfering substances. Regarding their release effect towards resins or adhesive substances, the inner tube films known to date are, by and large. in need of improvement.
In addition, the mechanical properties of state-of-the-art PE/PA or PE/AP/PA films used as inner tube films such as their (continued) tear resistance & strength, elasticity, splicing tendency, impact resistance or puncture resistance can still be potentially improved. Something similar occurs with other known tubular films.